A video disc reproducing system wobbles the reading beam across the storage track of the disc and the outputs of two photocells are added to develop both the information signal and a radial beam tracking signal employed to maintain tracking registration of the beam and the storage track. The outputs...http://www.google.com.tw/patents/US3932700?utm_source=gb-gplus-share專利 US3932700 - Focus tracking registration for optical reproducing systems
